AU2006322864A1

AU2006322864A1 - Electrolytic capacitors comprising means in the form of a multilayer polymeric sheet for the sorption of harmful substances

Info

Publication number: AU2006322864A1
Application number: AU2006322864A
Authority: AU
Inventors: Marco Amiotti; Luca Toia
Original assignee: SAES Getters SpA
Current assignee: SAES Getters SpA
Priority date: 2005-12-06
Filing date: 2006-11-30
Publication date: 2007-06-14
Anticipated expiration: 2026-11-30
Also published as: ITMI20052344A1; US20090225496A1; WO2007066372A3; EP1958222B1; CN101297383A; KR101237874B1; CN101297383B; WO2007066372A2; ATE551706T1; WO2007066372B1; EP1958222A2; CA2622970A1; JP2009518845A; AU2006322864B2; US7663865B2; KR20080046263A

Abstract

Electrolytic capacitors are provided having an airtight housing, electrodes immersed in an electrolytic solution, electrical contacts connected to the electrodes, and a device for sorption of harmful substances. The device is made of a multilayer polymeric sheet (10), which is formed of an inner layer (12) of polymeric material, containing particles of one or more getter materials (11) for sorption of the harmful substances, and at least one protective layer (13) of a polymeric material impermeable to the electrolyte. All of the polymeric materials are permeable to the harmful substances.

Description

WO 2007/066372 PCT/IT2006/000831 -1 "ELECTROLYTIC CAPACITORS COMPRISING MEANS IN THE FORM OF A MULTILAYER POLYMERIC SHEET FOR THE SORPTION OF HARMFUL SUBSTANCES" 5 The present invention relates to electrolytic capacitors containing means able to sorb the harmful substances created by such capacitors during their use. The present invention also relates to a method for the sorption of said substances. Known electrolytic capacitors, e.g. EDLC supercapacitors (Electrochemical Double Layer Capacitor), are essentially comprised of an airtight housing, wherein 10 electrodes typically formed of metal sheets are arranged, the electrodes being immersed in particular electrolytic solutions; the housing also contains gettering elements for the sorption of harmful substances, and electrical contacts communicating said electrodes with the outside of the capacitor. The electrolytic solutions are typically formed of a solvent and an ionic salt; in the 15 EDLC case, for example, acetonitrile and propylene carbonate are frequently employed as solvents, while tetraethylanmonium tetrafluoroborate is often used as a salt. During use, these solutions can create harmful substances, often in gaseous form, which can damage the capacitors even in an unrepairable manner; another possible source of harmful gases can be due to the desorption of some materials used inside the 20 capacitor. Carbon dioxide, carbon monoxide, hydrogen are among the most harmful gaseous species; while water, which is another species being particularly harmful, is typically present in liquid form inside the electrolytic solution. The problem of the sorption of harmful species inside the capacitors can be 25 tackled by adding one or more sorbing elements mixed in the electrolytic solution, or by means of non-mixed sorbing systems. The use of materials with a gettering action being mixed in the electrolyte can be accomplished by liquid sorbers; this solution is disclosed e.g. in patent application PCT/IT2006/000349 in the applicant's name. A second embodiment prescribes the use of solid sorbers being added to the electrolyte, as 30 described in JP 03-292712, wherein an additive including a particulate of platinum, palladium or alloys thereof is applied onto the sheets after these have been impregnated WO 2007/066372 PCT/IT2006/000831 -2 with the electrolytic solution; however, these sheets may have a very small thickness, in particular lower than 10 micrometers (pim), whereby they may be damaged by the particles contained in such a particulate due to their relatively large diameter, resulting in the risk of accidental short-circuits within the capacitor. 5 A system employing gas sorbers placed in delimited regions of the capacitor is described in patent application JP 2003-197487; in this case the sorbing material is used in the form of sheets of a polymeric material, such as polypropylene, as a support of the sorbing material; these sheets are directly contacted by the electrolytic solution. These types of solution are limited by the fact that the sorbing material, in 10 addition to have the function of sorbing the harmful substances produced within the capacitor, must be compatible with the electrolyte, i.e. it must be completely inert with respect thereto, in order to prevent its sorbing properties from being jeopardized, or even worse, in order to prevent that chemical species harmful for the correct operation of the capacitor are released as an effect of the reaction with the electrolyte; for example 15 the possible decomposition of the gas sorber could vary the electric conductivity of the electrolyte. Such a compatibility must be guaranteed by the sorber even after this has carried out its function by binding with the harmful species. In a first aspect thereof, the present invention relates to an electrolytic capacitor being able to overcome the problems still present in the prior art, and particularly 20 consists in an electrolytic capacitor comprising an airtight housing, electrodes being immersed in an electrolytic solution, electrical contacts, connected to the electrodes and a means for the sorption of harmful substances, characterized in that said means for the sorption of harmful substances is a multilayer polymeric sheet formed of an intermediate layer of polymeric material containing particles of one or more getter 25 materials for the sorption of said harmful substances, and at least one external protective layer of polymeric material being impermeable to the electrolyte, wherein all the polymeric materials are permeable to said harmful substances. The invention will be illustrated with reference to the annexed drawings, wherein: - Figure 1 shows in a partial cut-away view a first embodiment of means for 30 the sorption of harmful substances in electrolytic capacitors; - Figure la is an enlargement of a detail of Figure 1; WO 2007/066372 PCT/IT2006/000831 -3 - Figure 2 shows an alternative embodiment of means for the sorption of harmful substances in electrolytic capacitors; - Figure 3 shows a view of a portion of the walls of a electrolytic capacitor, to which a means for the sorption of har{nful substances is fixed; 5 - Figure 4 shows a cross sectional view of an electrolytic capacitor containing a means for the sorption of harmful substances, in the form of a multilayer polymeric sheet according to a first embodiment; and - Figure 5 shows a second embodiment of an electrolytic capacitor containing a means for the sorption of harmful substances, in the form of a multilayer 10 polymeric sheet. The size and the size ratios of the various elements shown in the drawings are not correct, having been altered in order to help the understanding of the same drawings. In order to manufacture the electrolytic capacitors of the invention it is necessary that the means for the sorption of harmful substances are provided with at least one 15 protective layer of polymeric material, i.e. permeable to the harmful species but impermeable to the electrolyte, covering at least one of the two main surfaces of the intermediate layer containing the getter particles. 'Figure 1 and the enlargement of a detail thereof in Figure 1 a, show in a partial cut away view, a multilayer polymeric sheet 10 for the sorption of harmful substances in 20 electrolytic capacitors, wherein getter material particles 11 are dispersed in a layer 12 of a polymeric material permeable to gases, which is in turn completely enclosed in a continuous layer 13 of a polymeric material being permeable to gases but impermeable to the electrolyte, thereby protecting the getter material from contact with the electrolyte. This allows a free choice of getter material, regardless of the type of 25 electrolyte used inside the capacitor. Alternatively, the protective polymeric coating covers only partially the inner polymeric layer containing the getter material. In a first embodiment according to this modality, represented in Figure 2, the means for sorption of harmful substances is in form of a multilayer sheet 20, comprising 30 a layer 22 of a polymeric material containing the getter material and two layers, 23 and 23', of protective polymeric material laid against' the two main surfaces of layer 22, but WO 2007/066372 PCT/IT2006/000831 -4 leaving unprotected the edge 24 of layer 22. The small dimensions of surface 24 exposed to the electrolyte do not jeopardize the functionality of the whole system. Finally, in case the means for the sorption of harmful substances is laid against an inner wall of the casing of the capacitor, there is no need for a protective layer between 5 the layer containing the getter material and such innerwall, the protection being only necessary for the surface facing the electrolyte. This situation is represented in figure 3, showing a portion of the casing, 30, of a capacitor (a flat wall is exemplified, but any other useful shape is possible); against an inner surface, 31, of said casing, is adhered (e.g. by means of melt welding) a means 32 for the sorption of handful substances; 10 means 32 is formed by a layer 33 containing getter particles, and a protective layer 34 permeable to the harmful substances but not to the electrolyte. Means 32 is represented in a configuration similar to what described for sheet 20, namely, with the edge 35 of layer 33 exposed to the electrolyte, but layer 34 could be fixed to surface 31 along the whole perimeter of layer 33, so as to completely surround and protect this latter (this 15 last alternative embodiment is not shown in the drawings). Layers of polymeric material containing particles of getter material are described in international patent application WO 2005/107334A1 concerning the purification of the inner atmosphere of electroluminescent organic screens. However, such layers containing getter material are without a protective polymeric layer, which is of key 20 importance to carry out the present invention. Sheets formed of layers of polymeric material comprising getter material and a protective layers, being of polymeric material as well, are described in patent US 5,091,233; in this case these materials are used for the manufacturing of evacuated panels and the aim of the polymeric film protecting the getter material is to slow down 25 the permeation of gaseous substances, rather than carrying out a selective permeation protecting the same getter material as in the present invention. The inner polymeric layer containing the getter material may be manufactured through an extrusion process and subsequent rolling of a batch of material including the polymer in semisolid condition and particles of getter material as uniformly dispersed 30 therein as possible. In order not to jeopardize the plasticity characteristics of the layer containing the getter material, the weight percentage of the particles of one or more WO 2007/066372 PCT/IT2006/000831 -5 getter materials must not be higher than 95%, and in a preferred embodiment it must be lower than 85%. As to the materials forming the protective polymeric layer(s), the inventors have found that materials suitable for carrying out the invention are polytetrafluoroethylene 5 (PTFE) and polyolefins, in particular polyethylene and especially low-density polyethylene (LDPE). These materials are also suitable for the manufacturing of the polymeric layer containing the getter material; in a preferred embodiment, the same type of polymer is used both to manufacture the polymeric layer containing the getter material and to 10 manufacture the protective layer(s). The layers of polymeric material forming the multilayer sheet may be joined to one another by means of various processes widely known in the field, e.g. by means of multilayer extrusion, multilayer rolling or pressure die casting. The getter materials used in the means according to the invention are of various 15 kinds, depending on the harmful substances to be removed from the inside of the capacitor; the nature of these substances may be ascertained, for any kind of capacitor, by means of preliminary tests carried out analyzing the gas developed during operation by different types of capacitors without any mear11 for removing gases. When the harmful substance is hydrogen, it is possible to use non-evaporable 20 getter alloys, particularly the zirconium-vanadium-iron alloys described in patent US 4,312,669 and sold by the applicant under the name St 707, or the zirconium-cobalt-RE alloys (RE stands for Rare Earths) described in patent US 5,961,750 and sold by the applicant under the name St 787; it is also possible to use unsaturated organic compounds (possibly along with hydrogenation catalysts), zeolites with a silver deposit 25 or carbon nanotubes; finally, it is possible to use materials that react with hydrogen forming water, such as palladium oxide (PdO) or cobalt(II,III) oxide (C030 4 ), in combination with H20 sorbers. In case the harmful substance is H20, as getter material is possible to use alkaline earth metals oxides (preferred is calcium oxide), boron oxide or zeolites. 30 In case the harmful substance is carbon dioxide, suitable getter materials are lithium hydroxide, alkaline-earth metals hydroxides, or lithium salts such as LiXOy, WO 2007/066372 PCT/IT2006/000831 -6 where X is chosen among zirconium, iron, nickel, titanium and silicon and y is comprised between 2 and 4. In case the harmful substance is carbon monoxide, it is possible to use the cobalt(II,III)oxide (C030 4 ), copper(II) oxide (CuO), or potassium permanganate 5 (KMnO 4 ), preferably along with a CO 2 sorber. The means for the sorption of harmful substances for use in the electrolytic capacitors of the present invention may also include more than one getter material, depending on the harmful substances needed to be removed from the capacitor. For example, in capacitors where the solvent is acetonitrile, hydrogen production mainly 10 occurs, whereby it is advisable to use a composition with more getter material for such-a gas, whereas in the case where the solvent is propylene carbonate, a larger amount of particles must be used to sorb CO and C0 2 . The particles of getter material must have a grain size lower than 150 pm, preferably between 25 and 50 pm in the case of non-evaporable getter alloys, between 15 about I and 25 pm in the case of salts, oxides or zeolites, and below 1 mm when using carbon nanotubes or organic compounds. The thickness of the two polymeric layers forming the getter system is another very relevant parameter. In particular, the thickness of.the polymeric layer containing the getter material must be comprised between 5 and 200 tm, depending on the grain 20 size of the particles of getter material (in particular, this thickness must be higher than the dimension of the getter particles), and preferably between 10 and 100 gm, while as to the external protective layer, its thickness may be comprised between 1 and 50 jim, preferably between 2 and 20 ptm. The electrolytic capacitors of the present invention are preferably, manufactured 25 by placing the getter system for the sorption of harmful substances along one or more internal walls of the airtight housings, or portions thereof. For example, Figure 4 shows a cross sectional view of an electrolytic capacitor 40 of cylindrical shape, comprising an airtight housing 41 inside which are present electrodes in the form of thin sheets coiled to form a spiral 42 immersed in a liquid 30 electrolyte (not shown). A multilayer sheet 43 is arranged against the inner wall of such a capacitor; the sheet may be of any of the kinds described with reference to figures 1, 2 WO 2007/066372 PCT/IT2006/000831 -7 and 3. The electrolytic capacitor shown in Figure 4 shows a cylindrical geometry, but such a geometry is not compulsory for the manufacturing of the invention, for instance another geometrical shape preferred for these capacitors is the parallelepiped one. In Figure 5 another preferred geometry for the EDLC capacitors is shown; in this 5 case the structure of the electrolytic capacitor 50 includes a plurality of electrodes 52, 52', ... , (only the outermost two shown in the girawing for the seek of clarity) in the form of parallel metal plates, immersed in an electrolytic solution (not shown). On one side of such a capacitor the means 53 for the sorption of harmful gases is arranged. The electrical contacts 54 and 54' communicate the electrodes with the outside of the 10 airtight housing 51 of the electrolytic capacitor.

Claims

1. Electrolytic capacitor (40; 50) comprising an airtight housing (41; 51), electrodes (52, 52', ...) immersed in an electrolytic solution, electrical contacts (54; 54') connected to the electrodes and a means (10; 20; 32; 43; 53) for the sorption of harmful substances in the form of a multilayer polymeric sheet formed of an inner layer (12; 22; 33) of polymeric material containing particles (11) of one or more getter materials for the sorption of said harmful substances, and at least one external protective layer (13; 23, 23'; 34) of polymeric material impermeable to the electrolyte, wherein all the polymeric materials are permeable to said harmful substances, characterized in that: - when said harmful substances comprise hydrogen, said getter material is selected among non-evaporable getter alloys, unsaturated organic compounds, zeolites with a silver deposit, carbon nanotubes, palladium oxide or cobalt(II,III) oxide; - when said harmful substances comprise H 2 0, said getter material comprises one or more compounds among alkaline-earth metal oxides, boron oxide and zeolites; - when said harmful substances comprise CO and said getter material comprises one or more compounds among the following: cobalt(II,III) oxide, copper(II) oxide and potassium permanganate.

2. Electrolytic capacitor according to claim 1, characterized in that said external protective layer completely covers said inner layer apart at most the edge (24; 35) of said inner layer.

3. Electrolytic capacitor according to claim 1, wherein said particles of one or more getter materials have a size lower than 150 gm.

4. Electrolytic capacitor according to claim 1, wherein the weight percentage of said particles of one or more getter materials in said inner layer is lower than 95%.

5. Electrolytic capacitor according to claim 4, wherein said weight percentage is lower than 85%.

6. Electrolytic capacitor according to claim 1, wherein said protective layer and said inner layer of polymeric material containing particles of one or more getter materials are made A ME fl1k Ih EEr r 01 1 1r9I IA r'9fO I r- Ad%' WO 2007/066372 PCT/IT2006/000831 12 of a material chosen between a polyolefin and polytetrafluoroethylene (PTFE).

7. Electrolytic capacitor according to claim 6, wherein said polyolefin is low-density polyethylene.

8. Electrolytic capacitor according to claim 6, wherein the protective polymeric layer and the inner polymeric layer containing particles of one or more getter materials are made of the same polymeric material.

9. Electrolytic capacitor according to claim 1, wherein said non-evaporable getter alloys are chosen between zirconium-vanadium-iron alloys and zirconium-cobalt-Rare Earth alloys.

10. Electrolytic capacitor according to claim 9, wherein the particles of said getter material have a size comprised between 25 and 50 pim.

11. Electrolytic capacitor according to claim 9, further comprising a hydrogenation catalyst.

12. Electrolytic capacitor according to claim 9, wherein said getter material is used together with a getter material for the removal of H 2 0.

13. Electrolytic capacitor according to claim 1, wherein said alkaline-earth metal oxide is calcium oxide.

14. Electrolytic capacitor according to claim 1, wherein said getter material is used together with a getter material for the removal of CO 2 .

15. Electrolytic capacitor according to claim 1, wherein the thickness of said at least one protective polymeric layer is comprised between 1 and 50 pm.

16. Electrolytic capacitor according to claim 15, wherein said thickness is comprised between 2 and 20 pm.

17. Electrolytic capacitor according to claim 1, wherein said inner layer of polymeric material containing the getter material has a thickness comprised between 5 and 200 Rm.

18. Electrolytic capacitor according to claim 17, wherein said thickness is comprised between 10 and 100 jm.

19. Electrolytic capacitor according to claim 1, wherein said multilayer polymeric sheet is placed along one or more internal walls of said airtight housing. A RMflLIEI"r CL=IJET IA I" TIfI E si fl WO 2007/066372 PCT/IT2006/000831 13 STATEMENT UNDER ART. 19(1) Claims 9, 12, 14, 15, 17 and 20 have been deleted and their content now forms the characterizing portion of the amended claim 1. Also claim 19 has been deleted. The other claims remain unamended, apart from the resulting changes in the relevant numbers and dependencies.